a. Field of the Invention
The present invention relates to a galvanic anode type cathodic protection apparatus which comprises cathodic protection sacrificial anodes as installed on a structure to be protected from corrosion (hereinafter called `the structure` for short), such as the inner side of a ballast tank of ship.
B. Description of the Prior Art
A galvanic anode type cathodic protection apparatus utilizing a sacrificial anode -- especially a core-inserted sacrificial anode -- for the purpose of protecting metal structures exposed to corrosive environment from electrochemical corrosion has hitherto been prevalently applied to the underground gas pipeline, harbor structures, ship hull, ballast tanks of tanker, etc.
In order words, for the purpose of preventing corrosion of metal structure laid in the sea or the ground, such as the hull of ocean-going ship, the tank of tanker, the pipeline network for petroleum, gas and water service, etc., the use of sacrificial anodes such as zinc, aluminum or magnesium as well as alloys thereof is prevalent. Most of these anodes are usually formed into a shape of cast block or slab with steel or copper core which is beforehand plated with zinc or cadmium, and the anode core is normally fixed on the structure by welding or bolting or such like, thereby electrically being connected with the structure. Besides, according to the prior art, the sacrificial anodes have been individually installed on the structure at considerable expenses for installation.
Nowadays, the structures as the object of corrosion prevention have become large-sized, coupled with getting complicated in construction. As a result, in the existing circumstances, the number of sacrificial anodes for use in a single corrosion preventive apparatus is on the increase, leading to a sharp increase in time and labor required for installing anodes. Particularly, the replacement of anodes at a place in the upper part of the structure where no staging for installation is available is too difficult to perform and even if the replacement is possible, it will require much time, labor and expense.
For instance, in the case of the upper part of bulkhead in the inside of a ballast tank, though the anode can be installed at the time of building the ship, there are instances where the position for installing the anode is shifted to the bottom of tank or installation thereof is dispensed with by taking into consideration the time and labor to be required for repairment or replacement of anodes and the cost of temporary staging, resulting in failure to obtain the effect of corrosion control as expected.
Meanwhile, from the view point of handiness of the anode and work efficiency in installing it within the tank, there are frequent occasions when it becomes necessary to limit the unit weight of anode. Under such circumstances, the number of anodes to be installed is inevitably increased. And, in the cases of harbor facilities and offshore structures, the anode installation work must be performed often under water, entailing much time for the work.
Such being the case, invention of an cathodic protection apparatus that will render it possible to install and replace the anode easily, safely, rapidly and economically has been strongly demand by the industrial world concerned.